First, I would like to apologize for the poor quality of my English, it’s not my main and I never learned it in school. I learned it on the internet, so I dont know all the subtleties of this language.

Hello everyone, I'll talk about the Motion Blur and errors that developers make when implementing it, I searched in this forum and it does not seem to me that such a topic has already been created so here it is !

What is motion blur and why our eyes creates it.

Motion blur is a blur that our eyes add on the object when the object is going too fast for our eyes to focus on it, our eyes add it so that we can have a sense of motion without seeing jerky movement (the framerate of the eye is not high enough for the motion of the object to be fluid enough).

In what circumstances should you add it to a video game.

If the frame rate is extremely high and the game is used on a screen with more than 120hz (it could be inconvenient with smaller frequency) it is necessary, if we can see an entirely clear tennis ball going at full speed on a frequency too high it can cause headaches and dizziness because the images on the screen are to close to the framerate of the eye, thus making the video credible enough for our brains to accept it as “real" but can’t manages to create the motion blur on the object because it does not move physically.

Where should you apply it.

On any object moving at such a high speed that it appears jerky on the screen.

This effect works especially well to accentuate the impression of speed we want to give to a movement, like a punch or slash with a sword, on stars when going full speed with a space ship, etc.

Where shouldn't you apply it.

On camera movement, and here's why:

When the eye changes is subject, it creates a motion blur all the way from the start angle to the end but instead of showing us this vagueness, the brain erases the visual memory we have of this instant and replaces it with x times the end frame. So we do not perceive the motion blur at all, only x time the same image.

To verify this, because I know that many of you might not believe me, take a clock, if you dont have one, here's one.

Look at something, now look at the clock and you will see that the first second is longer than the one following it.

I’ll end this by saying that this effect can be used in any type of video game with any aesthetic style, it’s an effect that adds more on credibility than realism.

Like any effect, it must be used sparingly because it could interfere with the readability of the gameplay.

I think a motion blur post-process filter is absolutely necessary for that cinematic feel.

I don't have much time right now to explain how motion-blur as a post-process in games evolved, but I can say it's got very sophisticated down to complex shaders that process each pixel based on its on-screen velocity.

A couple of articles on this (the latter is the most recent approach to this effect, with the best results):